Cleaning device and method for cleaning polishing cloths used for polishing semiconductor wafers

ABSTRACT

A cleaning device is used to clean a polishing pad and has a first cleaning system with a grinding wheel and a second cleaning system with a distributor for discharging a gas-water mixture at high pressure. The polishing pad, which is arranged on a polishing table, can be set in rotary motion, so that the surface sections that will be cleaned are first preliminarily cleaned by the grinding wheel and are then subjected to a second cleaning by the gas-water mixture of the distributor.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of copending International Application No. PCT/DE01/04082, filed Oct. 25, 2001, which designated the United States and was not published in English.

BACKGROUND OF THE INVENTION

[0002] Field of the Invention

[0003] The present invention relates to a cleaning device and to a method that includes using the cleaning device to clean polishing pads, in particular polishing cloths that are used for chemically mechanically polishing semiconductor wafers during a fabrication process.

[0004] In the semiconductor industry, the demand for increasingly smaller feature sizes and an increasing yield in semiconductor wafers means that, in addition to process control, a reduction in the defect density on the wafers is becoming increasingly important. During a process of patterning and processing a semiconductor surface, it is possible to provide for certain materials to be abraded using a polishing pad, for example, a polishing cloth, by chemical mechanical polishing or the like.

[0005] Examples of known devices used for this purpose are the IPEC/Westech 472, which is a device used specifically for the chemical mechanical polishing of silicon wafers. The polishing process carried out using this device is a single-wafer process in which the product side of the wafer is subjected to chemical mechanical polishing. However, the abraded material produced in this polishing process accumulates in the polishing pad. These accumulations of material may have adverse effects on the polishing of subsequent wafers, for example, as a result of forming scratches on the surface of these wafers. The problem arises in particular in the case of Cu processes, since contamination of a silicon wafer which is subsequently polished can lead to components on this silicon wafer failing.

[0006] To reduce contamination of subsequent wafers caused by material abraded from wafers that have been polished previously and to limit the load on the polishing pad caused by abrasion, the polishing pad has hitherto been changed very frequently. However, in general terms this constitutes a drawback, since the resultant costs and changeover times have a significant effect on the performance of the polishing process.

[0007] Therefore, it has already been proposed for the polishing pads used in the polishing process to be cleaned to remove the accumulated abraded material and residues of the slurry used in the chemical mechanical polishing. Published German Patent Application DE 197 37 854 A1, which is hereby incorporated by reference in the content of the present application, describes a device for cleaning a polishing pad, for example, a polishing cloth for polishing wafers. This device is substantially formed by a distributor for discharging a gas-water mixture at a high pressure. The gas-water mixture is atomized and sprayed onto the polishing pad that is to be cleaned via nozzles that are arranged on the outlet side of the distributor. Furthermore, there is a blasting nozzle for blasting a targeted jet of water onto the polishing pad that is to be cleaned. The targeted jet of water is likewise discharged from the blasting nozzle at a high pressure. Although in principle this cleaning device allows thorough cleaning of the surface of the polishing pad, it has been found that the cleaning process is ineffective, since particles of materials which have become fixed to the polishing pad can only be removed by a relatively high consumption of the gas-water mixture.

SUMMARY OF THE INVENTION

[0008] It is accordingly an object of the invention to provide a cleaning device and a method of using the cleaning device to clean a polishing pad, which overcomes the above-mentioned disadvantages of the prior art apparatus and methods of this general type.

[0009] In particular, it is an object of the invention to provide a cleaning device for cleaning polishing pads, in particular polishing cloths, which enables the surface of the polishing pads to be cleaned thoroughly and effectively.

[0010] With the foregoing and other objects in view there is provided, in accordance with the invention, a cleaning device for cleaning a polishing pad. The cleaning device includes: a first cleaning system including a grinding wheel; and a second cleaning system including a distributor for discharging a gas-water mixture under high pressure. The distributor has an elongate shape. The distributor has an outlet side with a plurality of nozzles. The distributor is positionable above a surface of the polishing pad that will be cleaned such that the distributor is located next to an axis of rotation of the polishing pad. The distributor extends in a longitudinal direction not aligned with the axis of rotation of the polishing pad.

[0011] The present invention is based on the fundamental idea of cleaning the polishing pads using substantially two cleaning systems. A first cleaning system is-responsible for a preliminary or rough cleaning of the surface of the polishing pad and a second cleaning system is responsible for further cleaning of the surface. The first cleaning system substantially includes a rotating grinding wheel for grinding down the surface of the polishing pad. By contrast, the second cleaning system substantially includes the distributor for discharging a gas-water mixture onto the surface of the polishing pad, which is known per se in the prior art and is described in the abovementioned Published German Patent Application DE 197 37 854 A1.

[0012] A corresponding method for cleaning the surface of the polishing pad can take place in such a way that, in a first cleaning step, first of all, the entire surface of the polishing pad is ground down, and then, in a second cleaning step, the surface is acted on by the gas-water mixture under high pressure. If appropriate, the two cleaning steps can be carried out alternately a number of times in succession.

[0013] In an advantageous embodiment of the cleaning method, however, the two cleaning steps are carried out simultaneously, in which case, simultaneously, different sections of the surface are either ground down or acted on by the gas-water mixture, and the polishing pad is set in rotary motion about a main axis, so that substantially each section of the surface is subjected to both cleaning steps at least once.

[0014] For this purpose, the cleaning device is preferably designed in such a way that the polishing pad that will be cleaned can be positioned in such a manner that the surface of the polishing pad that will be cleaned faces the grinding wheel and the outlet side of the gas-water mixture from the distributor. The grinding wheel and the distributor are each secured to holding arms in such a manner that they are located opposite different sections of the surface of the polishing pad. The polishing pad is mounted such that it can rotate about a main axis. In this case, at least one of the holding arms for the grinding wheel and the distributor can be arranged pivotably. In addition, a spray nozzle for washing off abrasive particles that have been removed from the surface of the polishing pad by the grinding wheel can be secured to the holding arm of the grinding wheel.

[0015] The cleaning device may additionally include a liquid nozzle, through which a further section of the surface of the polishing pad can be acted on by a liquid, in particular water. As a result, the surface of the polishing pad, in particular a surface section which has just been polished with a gas-water mixture, can be washed using a targeted water jet from the liquid nozzle.

[0016] Since the polishing pads that are used for chemical mechanical polishing processes in semiconductor process technology in many cases are round, substantially in the shape of the semiconductor wafer, the cleaning device is preferably designed in such a way that a circular polishing pad can be mounted in it for a cleaning process. The circular polishing pad is preferably placed on a rotatably mounted base. In this case, the grinding wheel, the distributor and if appropriate the liquid nozzle can then be arranged at different circumferential sections of the circular polishing pad. The arrangement of these components and the rotary motion of the polishing pad are preferably such that the surface sections are subjected to a cleaning treatment by the grinding wheel, are then acted on by the gas-water mixture, and finally are washed by the targeted water jet from the liquid nozzle.

[0017] Both the grinding wheel and the distributor may be secured to their respective holding arms in such a manner that they can be displaced along the holding arm.

[0018] The distributor for discharging a gas-water mixture may be designed as described in the abovementioned Published German Patent Application DE 197 37 854 A1. The entire content of this document, but in particular the sections which relate to the structure of the distributor for the gas-water mixture and the provision of the gas-water mixture in the distributor, are hereby incorporated by reference into the present application. In particular, a gas feed line and a water feed line are arranged on the inlet side of the distributor. The individual components of the gas-water mixture are fed into the distributor from different sources through the water feed line and the gas feed line. On an outlet side of the distributor, there is a multiplicity of nozzles that are used to discharge the gas-water mixture to the outside and/or to atomize this mixture.

[0019] The cleaning device according to the invention and the corresponding cleaning method enable abraded particles which are located on the polishing pad to be removed from the polishing pad in a way which is simultaneously thorough and effective. At the same time, the risk of contamination to wafers which are subsequently to be processed as a result of abrasion from wafers which have previously been polished is greatly reduced. The fact that first of all each surface section which is to be cleaned is subjected to preliminary cleaning by being ground down by means of the grinding wheel and is only then subjected to further cleaning by means of the distributor allows the cleaning process as a whole to be carried out very efficiently and the consumption of the gas-water mixture for the distributor to be reduced.

[0020] With the foregoing and other objects in view there is provided, in accordance with the invention, a method for cleaning a polishing pad. The method includes: providing the cleaning device that has been described above; positioning the distributor above a surface of the polishing pad that will be cleaned such that the distributor is located next to an axis of rotation of the polishing pad and a longitudinal direction of the distributor is not aligned with the axis of rotation of the polishing pad; and simultaneously or alternately, grinding down the surface of the polishing pad and directing the gas-water mixture under high pressure onto the surface of the polishing pad.

[0021] Other features which are considered as characteristic for the invention are set forth in the appended claims.

[0022] Although the invention is illustrated and described herein as embodied in a cleaning device for cleaning polishing cloths used for polishing semiconductor wafers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

[0023] The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a diagrammatic cross-sectional view of an exemplary embodiment of a cleaning device; and

[0025]FIG. 2 is a plan view of the cleaning device shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is diagrammatically shown, a cross section through an exemplary embodiment of a cleaning device for cleaning a polishing cloth 12 arranged on a polishing table 11. FIG. 2 shows a plan view of the cleaning device, illustrating the arrangement of the individual cleaning elements relative to one another and relative to the surface of the polishing cloth 12 that will be cleaned.

[0027] The cleaning device substantially includes a first cleaning system 5 for preliminarily cleaning the surface of the polishing pad 12 and a second cleaning system 2 for carrying out further cleaning. The first cleaning system 5 includes a circular grinding wheel 50 which is set in rotary motion during the cleaning operation. The grinding wheel 50 is secured to a pivotable holding arm 51 and can be displaced along the holding arm 51 (See FIG. 2 which shows the grinding wheel depicted in dashed lines at another position along the holding arm). At the start of a cleaning operation using the first cleaning system 5, the holding arm 51 is pivoted in so that the grinding wheel 50 is positioned above the surface of the polishing pad 12, whereupon the grinding wheel 50 is placed onto the polishing pad 12 with a defined pressure. The grinding wheel 50 is a circular wheel that is provided with a special, rough diamond-coated surface and roughens the surface of the polishing pad 12 resulting from its rotary motion. In addition a spray nozzle 52 (See FIG. 2) is secured to the holding arm 51. The spray nozzle 52 uses a liquid jet 52A to wash the abrasive particles that have been loosened from the polishing pad 12 by the roughening operation of the surface of the grinding wheel 50.

[0028] The second cleaning system 2 substantially includes a distributor 20 that is secured to a holding arm 25 (See FIG. 2). In the present exemplary embodiment, the holding arm 25 is arranged immovably. However, it may also be provided in such a way that the holding arm 25 of the second cleaning system 2 is also pivotable. On its outlet side 22, the distributor 20 has a multiplicity of nozzles 23. A gas feed line 40 and a water feed line 41 are arranged on the inlet side 21 of the distributor 20. The gas feed line 40 is connected to a nitrogen source (not shown), while the water feed line 41 is connected to a water source (not shown). The flow rates in the lines 40, 41 can be set by using corresponding valves 42, 43, for example, manually actuated valves. To generate a suitable pressure in the gas feed line 40 and the water feed line 41, there is a compressed-air source or other inert-gas source (not shown), which is connected via a compressed-air control device 44 and in particular by device of a compressed-air control device 44 a and a valve 45, to the water feed line 41, and via a compressed-air control device 44 b and a valve 46 to the gas feed line 40.

[0029] Deionized water under high pressure is mixed with ultrapure nitrogen in the distributor 20 of the second cleaning system 2, and the gas-water mixture is sprayed through the nozzles 23 in a targeted manner onto the surface of the polishing pad 12. By using a suitable setting of the valves 42 and 43, a defined incoming flow of nitrogen is set in the gas feed line 40 and a defined incoming flow of deionized water is set in the water feed line 41. The components located in the lines 40 and 41 are acted on by compressed air via the compressed-air control devices 44, 44 a, 44 b and a corresponding position of the valves 45, 46, so that the components, when they enter the distributor 20, are in each case at a pressure of, for example, 413.7 kPa (60 psi). After they have entered the distributor 20 at its inlet side 21, the components are mixed to form the gas-water mixture, for example, at the pressure mentioned. Then, the mixture is sprayed through the slot nozzles 23 onto the polishing cloth 12 that will be cleaned. The atomization of the deionized water and of the nitrogen just before they are discharged from the spray nozzles 23 results in the production of extremely small, highly effective drops having a kinetic energy which leads to loosening the particles which have become jammed and blasting the particles out of the polishing cloth 12.

[0030] Furthermore, the cleaning device has a blasting nozzle 30, from which a targeted water jet 30A is directed onto the polishing cloth 12 at an acute angle of less than 45°. The targeted water jet 30A is likewise at an elevated pressure. The targeted water jet 30A washes the particles that have been detached by the distributor 20 off of the surface of the polishing pad 12. This has the advantage that cleaning is achieved without damage to the very sensitive polishing pad surface.

[0031] In order, for example, for residues of a CMP (chemical mechanical polishing) process on the polishing pad 12 to be eliminated as effectively as possible, the two cleaning systems 2 and 5 can be used in parallel. In this case, first of all, the grinding wheel 50 is used to carry out intensive preliminary cleaning. A second intensive cleaning step is then carried out by the distributor 20. For this purpose, the polishing pad 12, which is arranged on the rotatable polishing table 11, is set in rotary motion in the counterclockwise direction (as indicated in FIG. 2 by the reference character 12 a). The distributor 20 has been designed in such a way that the spray area cleans the rotating polishing pad 12 over a length of 130 mm. The direction of rotation of the polishing table 11 is matched to the arrangement of the cleaning elements, i.e. the grinding wheel 50, the distributor 12, and the blasting nozzle 30. A section which has been cleaned by the grinding wheel 50 is inevitably, on account of the rotary motion, guided under the blasting area of the distributor 20, at which time the second cleaning step takes place, after which the particles which have been detached are washed off of the surface of the polishing pad 12 by the water jet 30A from the blasting nozzle 30.

[0032] In an alternate embodiment, it is also possible for the holding arm 25 of the second cleaning system likewise to be pivotable and initially to be in a pivoted-out position. The two cleaning steps may be carried out separately, in which case, first of all, in a first cleaning step, substantially the entire surface of the polishing pad 12 is ground down by the grinding wheel 50 that is secured to the holding arm 51 that has been pivoted in. After the first cleaning step has been carried out, the holding arm 51 of the first cleaning system can then be pivoted away and the holding arm 25 of the second cleaning system can be pivoted in, whereupon substantially the entire surface is subjected to a second cleaning step as a result of the surface being acted on by the gas-water mixture from the distributor 20. 

We claim:
 1. A cleaning device for cleaning a polishing pad, comprises: a first cleaning system including a grinding wheel; and a second cleaning system including a distributor for discharging a gas-water mixture under high pressure; said distributor having an elongate shape; said distributor having an outlet side with a plurality of nozzles; said distributor positionable above a surface of the polishing pad that will be cleaned while located next to an axis of rotation of the polishing pad; and said distributor extending in a longitudinal direction not aligned with the axis of rotation of the polishing pad.
 2. The cleaning device according to claim 1, wherein: the polishing pad is positionable such that the surface of the polishing pad faces said grinding wheel and said outlet side of said distributor; said first cleaning system includes a holding arm for positioning said grinding wheel opposite a first section of the surface of the polishing pad; said second cleaning system includes a holding arm for positioning said distributor opposite a second section of the surface of the polishing pad; and said polishing pad is mounted to rotate about the axis of rotation.
 3. The cleaning device according to claim 2, wherein at least one holding arm, which is selected from a group consisting of said holding arm of said first cleaning system and said holding arm of said second cleaning system, is pivotable.
 4. The cleaning device according to claim 2, further comprising: a spray nozzle secured to said holding arm of said first cleaning system; said spray nozzle for washing off abrasive particles that have been removed from the surface of the polishing pad by said grinding wheel.
 5. The cleaning device according to claim 2, further comprising a liquid nozzle configured for applying a liquid to a third section of the surface of the polishing pad.
 6. The cleaning device according to claim 5, wherein the liquid is water.
 7. The cleaning device according to claim 1, in combination with the polishing pad, wherein: the polishing pad is a substantially circular polishing pad; and said grinding wheel and said distributor are configured at different circumferential sections of the polishing pad.
 8. The cleaning device according to claim 1, in combination with the polishing pad, wherein: the polishing pad is a substantially circular polishing pad; the cleaning device includes a liquid nozzle that is configured to apply a liquid to the surface of the polishing pad; and said grinding wheel, said distributor, and said liquid nozzle are configured at different circumferential sections of the polishing pad.
 9. The cleaning device according to claim 1, in combination with the polishing pad, wherein the polishing pad is a polishing cloth.
 10. A method for cleaning a polishing pad, which comprises: constructing a cleaning device from a first cleaning system having a grinding wheel, and a second cleaning system having a distributor for discharging a gas-water mixture under high pressure; configuring the distributor with an elongate shape and configuring the distributor with an outlet side having a plurality of nozzles; providing the cleaning device for cleaning the polishing pad; positioning the distributor above a surface of the polishing pad that will be cleaned such that the distributor is located next to an axis of rotation of the polishing pad and a longitudinal direction of the distributor is not aligned with the axis of rotation of the polishing pad; and simultaneously or alternately, grinding down the surface of the polishing pad and directing the gas-water mixture under high pressure onto the surface of the polishing pad.
 11. The method according to claim 10, which comprises: simultaneously, grinding down a first section of the surface of the polishing pad and directing the gas-water mixture onto a second, different section of the surface of the polishing pad; and setting the polishing pad into rotary motion about the axis of rotation so that substantially each section of the surface of the polishing pad is subjected to both the grinding down and the gas-water mixture at least once.
 12. The method according to claim 10, which comprises first grinding down the surface of the polishing pad and subsequently directing the gas-water mixture onto the surface of the polishing pad.
 13. The method according to claim 10, which comprises alternately grinding down the surface of the polishing pad and subsequently directing the gas-water mixture onto the surface of the polishing pad a number of times in succession.
 14. The method according to claim 10, which comprises washing the surface of the polishing pad with a targeted water jet.
 15. The method according to claim 10, which comprises using a targeted water jet to wash a surface of the polishing pad that had shortly beforehand been acted on by the gas-water mixture. 